The invention relates to improvements in so-called pull-type friction clutches. A pull-type clutch is constructed and assembled in such a way that it is disengaged to interrupt the transmission of torque between its input and output elements by pulling the clutch engaging/disengaging part or parts in a direction away from the clutch disc or clutch plate and against the resistance of one or more springs or other biasing means. In many pull-type friction clutches, the clutch engaging/disengaging means and the biasing means constitute a single part, particularly a diaphragm spring. The prongs of the diaphragm spring are affixed to a connecting device, such as a dished or disc-shaped element, which must be subjected to a pull in order to disengage or deactivate the friction clutch. The radially outer portion of the diaphragm spring engages the cover or another part of the friction clutch, and a radially inner portion of the diaphragm spring engages an axially moveble pressure plate of the friction clutch. The situation is analogous in so-called lever-actuated pull-type friction clutches wherein the biasing means and the engaging/disengaging means constitute separate parts.
Pull-type friction clutches exhibit a number of important advantages over the so-called push-type friction clutches. However, when a conventional pull-type friction clutch is used in a motor vehicle to serve as a means for establishing or interrupting a torque transmitting connection between the output element (e.g., a crankshaft) of an internal combustion engine and the input element of a power train (such as the input shaft of a variable-speed transmission), the establishment and interruption of an operative connection between the engine and the power train are much more complicated than in the case of a push-type friction clutch.
German Pats. Nos. 26 13 952 and 26 39 766 propose the establishment of a connection between a pull-type friction clutch on the one hand, and the engine and the power train of a motor vehicle on the other hand. The power train carries a guide member which can be tracked by an axially movable follower. An antifriction bearing is installed between the clutch disengaging means (constituted by the prongs of a diaphragm spring) and the follower. The bearing has a first race which rotates with the diaphragm spring and a second race which does not rotate and is mounted on the follower. The patented pull-type friction clutches further comprise at least one connector between the disengaging means and the guide member. The latter is an elongated tube which is carried by the power train, and the follower is a sleeve which is shiftable along the tube by a forked actuator. The patents also propose to employ a follower which constitutes the piston of a hydraulic motor whose cylinder constitutes the guide member.
The means for connecting the engine with the power train comprises at least one male coupling member which can be caused to penetrate into a recess or space and to engage a retaining member which cooperates with the male coupling member to prevent separation of first clutch components on the engine from second clutch components on the power train. The first components can be mounted on the engine, and the second components can be mounted on the power train before such first and second components are coupled to each other. The male coupling member can comprise a split ring, one or more spherical parts or one or more spreadable jaws or claws, and this coupling member is constructed and mounted in such a way that it automatically engages the retaining member or members in response to movement of the engine and power train to predetermined positions relative to each other or in response to the application of an external force, such as by the forked actuator of the clutch disengaging means. The aforementioned patents fail to disclose or suggest a system which would facilitate repeated rapid and convenient separation of the engine and the power train from each other or repeated rapid and convenient reconnection of the engine and of the power train to one another.
A modified system for assembling a pull-type friction clutch between an engine and a power train is disclosed in published French patent application No. 2 588 337 and in published European patent application No. 0 164 871. The engine and the power train can be automatically coupled to each other in a manner as disclosed in the aforediscussed German patents. The connecting or coupling means comprises a ring which can be caused to snap into a groove or recess. The disengagement or uncoupling can be carried out automatically and involves axial movement of a sleeve in a direction counter to that which is required to disengage the friction clutch. Otherwise stated, uncoupling of the engine from the power train must be preceded by a movement of the sleeve in the direction of movement of the sleeve in response to wear upon the friction linings and/or other parts of the clutch plate which is installed between the flywheel and the pressure plate of the friction clutch. This entails a number of serious drawbacks. For example, if the force which is applied to connect the engine with the power train (such force must be applied in the direction of the application of force to disengage the assembled friction clutch), the parts to be connected to each other are likely to advance beyond their intended positions with the result that the actual coupling is immediately followed by uncoupling. The published French patent application proposes a coupling which can be used to reconnect immediately following disconnection without any interference from the outside. However, such interference is necessary in accordance with the proposal which is disclosed in the published European patent application. Thus, if the connection between the clutch components on the engine and the clutch components on the power train is interrupted, the engine and the power train must be fully separated from each other prior to reestablishment of a connection between the two sets of components. Unintentional separation can take place in the motor vehicle while the vehicle is in actual use, for example, as a result of pronounced vibrations and/or other undesirable stray movements. This can result in excessive movement of certain parts between the two sets of clutch components beyond their operative positions (as seen in the direction of engagement of the friction clutch). Such excessive movement can also take place when the clutch pedal is permitted to perform certain snap-type movements or when the foot of the operator happens to slip off the clutch pedal. The inertia of those parts which are caused to move as a result of the just described improper or unintended manipulation of the clutch pedal is likely to cause excessive movements of the coupling elements beyond their optimal positions to thus initiate accidental uncoupling of clutch components on the engine from the clutch components on the power train. The consequences of accidental uncoupling are or can be so serious that the just described pull-type friction clutches have failed to gain acceptance in the relevant industries.
A further mode of installing a pull-type friction clutch between the engine and the power train of a motor vehicle is disclosed in published European patent application No. 0 044 691, in published French patent application No. 2 540 585 and in published German patent application No. 35 39 889. A tubular guide is employed to effect radial displacements of coupling elements in response to movement of the engine and the power train relative to each other. The coupling elements are connected to each other in response to movement of the engine and the power train nearer to one another, and the connection between the coupling elements is interrupted when the engine and the power train move apart. A drawback of the just outlined proposals is that the parts to be connected to one another must assume accurately determined positions of axial alignment with one another. At the same time, the engine and the power train must be moved with reference to each other. The forked disengaging element and one group of components must be moved against the other group of components and must be maintained in accurately determined positions in order to ensure that the coupling elements can actually and properly engage one another. If the movements are not completed with a very high degree of accuracy, the aforementioned tubular member prevents the movements of the engine and the power train toward each other, and the application of additional force can result in damage to parts of the engine, power train and/or friction clutch. Another drawback of the just discussed proposals is that the forked actuator must perform large pivotal movements in order to shift the components to be coupled sufficiently close to each other before the engine and the power train are moved toward one another. As a rule, there is no room for such extensive pivotal movements of the fork. An additional drawback of the systems which are disclosed in the European patent application No. 0 044 691 and in the French patent application 2 540 585 is that the coupling elements engage the tubular guide during uncoupling of the engine from the power train; this results in the development of extensive friction and pronounced wear.
U.S. Pat. No. 4,778,039 granted Oct. 18, 1988 to Thomas Eliasson for "Friction clutch having premounted release bearing and premounted release mechanism" discloses a cylinder housing for an annular sleeve-like piston. A clutch release bearing carries a lock ring for attachment to a diaphragm spring before the engine and the gearbox are coupled to each other. The cylinder housing, the piston and a supporting tube for the piston are secured to the gearbox. The coupling mechanism is installed between the piston and the supporting tube. Prior to coupling of the gearbox to the engine, the piston is moved to a fully retracted position and is arrested in such position by a sleeve in cooperation with two stops. At such time, the sleeve is held on the supporting tube in a predetermined axial position by being confined between the two stops. When the connection of the engine and the gearbox to each other is completed, the piston is displaced from the retracted position in response to admission of a pressurized fluid into a chamber of the cylinder housing whereby the sleeve advances into a space within an annulus of rollers to push the rollers radially outwardly and to thus permit a wire ring to couple a flange to a shoulder. The sleeve continues to move axially in response to admission of additional fluid into the cylinder chamber to complete the establishment of a connection between the piston and the disengaging means. The connection between such parts remains intact as long as the engine and the gearbox remain connected to each other. During dismantling, i.e., during movement of the engine and the gearbox away from each other, the clutch release bearing remains attached to the diaphragm spring and causes the wire ring to pull the piston back to its retracted position. In the next step, one of the stops moves the sleeve away from the space within the rolling elements so that these elements can move radially inwardly, together with the wire ring, to thus complete the separation of clutch components on the engine from clutch components on the gearbox.
A drawback of the proposal of Eliasson is that uncoupling of the two halves of the friction clutch cannot be immediately followed by reconnection of such parts. The reason is that the one stop cannot reassume its original position and, therefore, the sleeve is also incapable of moving back to the locking position. The reestablishment of a proper connection between the two sets of parts is possible only by fully separating the engine from the gearbox and by thereafter fully dismantling the cylinder housing and the supporting tube.